The present invention relates to bone distraction and, more particularly, to an apparatus and method for osseous expansion of the skull and monitoring the same.
In human children, premature synostosis (fusion) of the coronal suture (the line of union of the two parietal bones with the frontal bone of the skull) causes a spectrum of craniofacial malformations ranging from simple brachycephaly to more severe deformities, such as Crouzon's and Apert's syndromes. The more severe deformities may also include premature fusion of the cranial base. These malformations display marked retrusion of the anterior cranial vault, anterior cranial base and facial skeleton. Left untreated, these deformities worsen, rather than improve, with continued skull growth.
There are several surgical procedures currently used to correct these anomalies. One method includes strip craniectomy release of all the fused sutures as early as possible in life to unharness the rapid brain growth of infancy. Theoretically, the skull then expands to proper relationship with the brain growth, thereby normalizing skull and facial growth. There is some evidence that this procedure has been successful when the fusion is simple and confined to the coronal suture system. Unfortunately, it has been unsuccessful in definitively correcting more extensive deformities such as Apert's and Crouzon's syndromes. Clinical evidence has indicated that in these severe anomalies, the forward push of the growing brain is unable to advance the retruded facial skeleton.
Thus, reconstructive advancement of the retruded facial skeleton in Apert's and Crouzon's syndromes is frequently deferred until early or mid-childhood when the facial skeleton is stronger and donor bone graft material present. Major craniofacial advancement is then accomplished by surgically disengaging and immobilizing the facial and frontal bones into a more anterior position with the use of multiple bone grafts. However, secondary operations are often required to maintain proper facial balance and dental occlusion.
A method that has been largely unexamined is to perform an initial interventive surgical release of the fused sutures and then apply continuous adjunctive external forces to the skull to distract the cranial bones. The forces should be congruent with the normal forward propulsive effort of the growing brain and be continuously regulated to guide the released craniofacial complex into the desired position. It is theorized that the widened intersutural spaces would be filled and stabilized with newly deposited bone.
Clinical techniques of facial sutural expansion have been confined mainly to the maxilla. Devices are available that apply forces across the mid-palatal suture to rapidly expand constricted maxillary dental arches and enlarge nasal airways. The devices deliver a transverse expansion force across the palate of children and adolescents by utilizing a jackscrew mechanism orthodontically fixed to the maxillary teeth. In adults, the immobile palatal sutures are surgically released prior to fixation of the device. The widened mid-palatal suture eventually fills with newly deposited bone. The facial sutural expansion method occurs most reliably when the periosteum enveloping the mid-palatal suture has been preserved.
Devices available for use with larger bone segments have generally focused on bone fixation to prevent skeletal relapse after fracture, rather than for the production of new bone between the segments. Fixation devices for stabilizing long bones typically include rods and coupling mechanisms attached to different parts of a fractured bone that hold the fractured bone parts together.
Devices are also available for use in the distraction of long, tubular bone sections that are externally fixed across a previously divided portion of the bone. The devices include pins or projections that extend deeply into the bone on either side of the divide and a mechanism for slowly expanding the device, thereby slowly elongating the bone. Once the desired length is achieved, the bone reconsolidates, resulting in both a solid union and lengthened limb.
Analogous application of such bone-expanding apparatus and methods have not been pursued in the field of surgical reconstruction of synostotic deformities. This delay may, in part, be due to the slow development of a suitable animal model for the study of craniosynostosis. Only relatively recently, such an animal model, rabbits, has been reported.
Furthermore, as stated above, the application of bone-expanding apparatus and methods to the area of skull expansion should include the careful application of force congruent with the normal forward propulsive effort of the growing brain which would require continuous regulation to guide the released craniofacial complex into the desired position. Regulation of bone growth necessitates a device for precisely monitoring the same. Radiographic techniques adequately provide an image of the skull and newly-formed bone, but precise monitoring of the bone expansion requires that a portion of the skull be repeatably placed in precisely the same position relative to the radiographic equipment.
Devices are available for humans that register an entire skull, with respect to medical equipment, by utilizing inserts for placement in the ears or contoured members that receive the head or facial features. These devices are not appropriate for monitoring skull expansion where a portion of the face or skull is being lengthened. Such devices would fail to register the skull with respect to one of the skull sections and, therefore, may not provide the preciseness required for tracking incremental bone growth. Additionally, devices created for adult humans may not be readily adapted for use with children, whose facial features may rapidly change, or for use with other animals, such as rabbits, for example, who do not have prominent facial features or ear openings placed for receipt of immobilizing projections. Therefore, there is a need for a registration and positioning device to be utilized with a skull fixation-distraction apparatus that is not dependent upon an outer feature of the patient being monitored.